Related Applications
This application is related to U.S. Ser. No. 454,109 titled Trailer Brake Anti-Swing System and Method, U.S. Ser. No. 454,096 titled Articulation Angle Sensor, U.S. Ser. No. 454,602 titled Tractor Trailer Anti-Trailer Swing System and Method, U.S. Ser. No. 454,095 titled Anti-Trailer Swing Control, and U.S. Ser. No. 454,110 titled Trailer Anti-Swing System and Method, all assigned to the assignee of this application and filed the same day (Dec. 20, 1989) as this application.
1. Field of the Invention
The present invention relates to a control system/method for controlling the braking force applied to the brakes of a towed subvehicle and/or the towing subvehicle in an articulated vehicle system, such as a tractor-semitrailer system, to prevent, arrest or to minimize and quickly recover from, the conditions known as brake induced trailer swing and/or jackknife.
2. Description of the Prior Art
Brake control systems for all types of vehicles, including heavy duty tractor-semitrailer trucks, to improve the stopping and vehicle stability thereof are, of course, well known in the prior art.
Brake systems of the anti-lock type, for all types of vehicles, are well known in the prior art. Briefly, these systems operate to maintain vehicle stability (i.e. acceptable transverse coefficient of friction of braked wheels) by maintaining the longitudinal slip of the braked wheels within predetermined limits. This usually requires modulating the braking forces on an individual wheel and/or individual axle basis to maintain at least some wheel rotation.
Examples of prior art anti-lock brake systems ("ABSs") may be seen by reference to U.S. Pat. Nos. 3,767,270; 3,768,872; 3,854,556; 3,893,696; 3,929,383; 3,929,382; 3,966,267; 4,392,202 and 4,591,213, the disclosures of all of which are hereby incorporated by reference.
Brakes systems which control braking to achieve a driver demand, sense driver demand in a "brake-by-wire" manner, sense coefficient of friction and modify brake forces accordingly, sense load on a wheel and modify braking effort accordingly, sense wheel slip and/or use electronic signals to achieve trailer brake response are also disclosed in the prior art as may be seen by reference to U.S. Pat. Nos. 4,140,352; 4,327,414; 4,494,199; 4,512,615; 4,545,240; 4,591,213; 4,606,586; 4,616,881; 4,648,663 and 4,768,840, the disclosures of which are hereby incorporated by reference.
Brake systems for heavy duty articulated vehicles such as tractor-semitrailer trucks are difficult to design as the loading and maintenance will vary in a truck, such as the loading on the tractor of a tractor-trailer which may comprise a tractor only, a tractor with an empty or lightly loaded trailer or a tractor with a heavily loaded trailer.
Further, tractor-semitrailers are, by their nature, capable of exhibiting certain unstable dynamic behaviors known as jackknife and trailer swing, each of which has its own characteristic cause, effect and appropriate sequence of corrective action. Jackknife is sometimes called "tractor brake caused jackknife" while trailer swing is sometimes called "trailer brake caused jackknife".
The dynamics of undesirable trailer articulation events, such as a jackknife event, are discussed in SAE Paper No. 710045, the disclosure of which is hereby incorporated by reference.
Various systems to prevent or minimize undesirable tractor trailer articulation have been proposed. These include mechanical devices such as chains or variable pivot resistance devices and also wheel speed sensors and anti-lock controls on the trailer per se. Examples of these prior art devices may be seen by reference to U.S. Pat. Nos. 3,618,983; 3,810,521; 3,894,773; 4,023,864, 4,405,145 and 4,620,717 the disclosures of which are hereby incorporated by reference.
The prior art devices were not satisfactory as the mechanical devices were somewhat slow to react, hindered required articulation during normal operation, required specially equipped/configured trailers and/or did not allow for a recovery from the locked-in condition. The anti-lock (ABS) type systems were not totally satisfactory as most existing trailers do not have ABS equipment, tractors are often driven with a variety of trailers and thus even if a trailer is provided with ABS equipment, it may not be compatible with the tractor ABS, providing all existing and future trailers with ABS equipment is prohibitively expensive and, under certain conditions, undesirable tractor trailer articulation may occur in the absence of the wheel lock conditions sensed and reacted to by existing ABSs.